This invention relates generally to apparatus for marking moving objects or substrates and more particularly, it relates to an improved laser marker apparatus for suitably coding paper labels, other substrates, printed material, plastic, painted surfaces and the like in which the number of dot positions in a vertical column is increased, thereby producing a higher resolution than has been traditionally available.
In U.S. Pat. No. 4,652,722 issued on Mar. 24, 1987, there is disclosed a laser marking apparatus which utilizes seven lasers for generating a 7-dot high character matrix and is assigned to the same assignee as the present invention. In particular, the laser beam from each source is directed by fixed mirrors through a single exit lens and then onto the surface to be marked. Individual laser mirrors each corresponding with one of the lasers are not movable and remain stationary during normal operation of the apparatus, even though they are adjustable for initial system alignment. The surface to be marked is positioned on a conventional conveyor or other device adapted to move the objects along a linear path adjacent the laser output head.
Each laser defines an essentially collimated energy source which is focused, by the exit lens, into a dot of a predetermined small size for precision marking of article surfaces as they pass the output head substantially in the focal plane of the exit lens. The incident angle of each of the seven laser sources onto the exit lens is initially adjusted to provide a plurality of closely spaced and focused dots which define a vertical column of seven light dots from which the character matrix can be obtained by modulation of the dots as the article or substrate is moved past the exit lens.
In order to produce higher printing quality for the character matrix, there is a need to generate a higher number of spots or dots for each vertical column. Simply increasing the number of lasers is impractical since the system costs would increase dramatically due to the increased components used. For example, if it was desired to provide a vertical column of 21 dots so as to improve the resolution by a factor of three, then there would be required an additional 14 lasers and associated components therefor. Also, it has been envisioned that the laser mirror 24 of the '722 patent used to reflect the beams from the respective mirrors 36a-36g via the delivery tube 18 to the exit lens 26 through the delivery tube 20 could be simply rotated so as to move the seven dots up or down to produce the 21 dots. However, this technique would require that the diameter of the exit lens 26 be increased by approximately two inches, thereby increasing substantially the system costs.
Accordingly, there is a need for an improved laser marker apparatus which has higher resolution but without increasing substantially its cost and complexity. The present invention represents an improvement over the aforementioned U.S. Pat. No. 4,652,722, which patent is hereby incorporated by reference.